The organic electroluminescence (hereinafter referred as “EL”) element that is one kind of organic semiconductor element is expected to find application to a wide range of fields such as illumination and display because it is the spontaneous light-emitting type of sheet light source manifesting thinness and lightness in build and wideness in angular field of view. The ordinary organic EL element is furnished with an element part resulting from stacking a transparent electrode as an anode, an organic layer containing at least a light-emitting layer, and a cathode sequentially in the order mentioned on a transparent substrate, for example, and is so configured as to extract from the back surface side of the substrate the light generated by feeding electric current to the organic layer.
Incidentally, since the organic layer partaking in the construction of the organic EL element is formed of a generally extremely unstable organic material, it produces a defect of being readily deteriorated by the influence of oxygen and moisture and entails the problem that the element suffers from shortness of the service life. The organic EL element, therefore, necessitates a countermeasure against the invasion of the interior of the element by oxygen and moisture existing in the ambience of the organic EL element.
The organic EL element generates not only light but also heat. When this heat accumulates inside the element, it induces deterioration of the organic material. Thus, the ability of the element to radiate heat constitutes an important matter. This problem of the generation of heat by the organic EL element tends to become more conspicuous in consequence of the enlarging the surface area of the light-emitting area as in the organic EL element for use in illumination, for example.
As the measure against the invasion by oxygen and moisture, the ordinary organic EL element, for example, adopts a configuration that has the element part containing the organic layer sealed with a sealing can made of metal or glass and has the gap inside the sealing can filled with an inert gas such as nitrogen gas
Since the organic EL element so configured as to effect necessary sealing with a sealing can is required to have the relevant components individually sealed with a sealing can, it entails numerous problems in terms of workability, productivity, and cost of production as well. Further, owing to the configuration requiring the periphery of the element part containing the organic layer to be sealed with a sealing can, the element entails the problem of rendering necessary cooling difficult. An attempt to attach a structural body with high thermal conductivity contiguously to the element part containing the organic layer with a view to enhancing the effect of thermal radiation, for example, is not easily implemented in the organic EL element possessing such a small thickness as several hundred nm and revealing poor mechanical strength. To do justice by all means, the effect of thermal radiation is very low because the inert gas with low thermal conductivity intervenes between the stacked body containing the organic layer and the sealing can, although the sealing can additionally fulfills the function of radiating the heat generated in the stacked body.
As structures for sealing an organic EL element without using a sealing can, the configurations that accomplish the sealing of a stacked body containing an organic layer by covering the stacked body with a protective film made of a resinous material have been proposed (refer to U.S. Pat. No. 3,334,408 and U.S. Pat. No. 3,405,335, for example). The invention described in U.S. Pat. No. 3,334,408 discloses a configuration that enables prevention of the invasion by oxygen and moisture with a multilayer structure consisting of a protective layer, a sealing layer, an internal air isolation layer, etc and the invention described in U.S. Pat. No. 3,405,335 discloses a configuration that attains the formation of a protective layer against mechanical damage by further superposing on a multilayer film a protective layer such as a plastic sheet or a metallic sheet.
Then, as heat-radiating structures for an organic EL element, the configurations that accomplish the thermal radiation by sealing an element part containing an organic layer with a protective film and attaching a radiator plate directly to the protective film have been proposed (refer to JP-A HEI 10-106746 and JP-A HEI 10-2756681, for example). The inventions described in JP-A HEI 10-107646 and JP-A HEI 10-275681 disclose a configuration that accomplish the thermal radiation by causing a radiator plate (plate of glass, resin, ceramic, or metal) to be tightly joined directly on a water-repellent protective film, for example.
However, the inventions disclosed in U.S. Pat. No. 3,334,408 and U.S. Pat. No. 3,405,335 mentioned above have a principal purpose in perfecting a film-sealing structure and pay virtually no consideration to thermal radiation. U.S. Pat. No. 3,405,335, for example, discloses a concept of superposing a plastic sheet or a metallic sheet on a film-sealing structure and does not assume at all the function of a radiator plate. Let alone, the optimization of a structure for effecting thermal radiation of high efficiency and a structure for reconciling film sealing and thermal radiation is not assumed at all.
The inventions described in JP-A HEI 10-106746 and JP-A HEI 10-275681 mentioned above, while disclosing a concept of providing a radiator plate, pay virtually no consideration to film sealing and merely go the length of making a simple statement that a radiator plate is provided. Naturally, the inventions disclosed in JP-A HEI 10-106746 and JP-A HEI 10-275681 have absolutely no mention of the optimization of a structure for reconciling film sealing and thermal radiation.
In the case of directly disposing a radiator sheet on a sealing film, the radiator sheet is ordinarily pasted to the sealing film by the use of an adhesive agent, for example. It has been unveiled that the environment prevailing in this case during the curing of the adhesive agent exerts an adverse effect on the organic EL element. When a photo-curing adhesive agent is used, for example, since the ultraviolet light radiated for the purpose of curing this adhesive agent irradiates the organic EL element at the same time, it causes deterioration of the organic substance in the organic EL element. When a thermosetting adhesive agent is used, since the curing thereof necessitates application of heat, the outgassing occurring during the heating infiltrates the sealing film and reaches the organic EL element part and likewise causes deterioration of the organic EL element part. The conventional technique has not recognized at all the adverse effect exerted on the organic EL element during the course of adhesion and has not taken any measure against the adverse effect.